1. Field of the Invention
The present invention relates to an electro-optic probe using an electro-optic element and a magneto-optic probe using a magneto-optic element.
2. Description of the Related Art
It is possible to observe the waveform of a measured signal by acting an electric field generated by measured signal on an electro-optic crystal, irradiating laser beam onto the electro-optic crystal, and observing the waveform of the measured signal by the state of polarization of the laser beam. In this case, the laser beam is given the form of light pulses and the measured signal then sampled, the observation can be made at an extremely high time resolution. The electro-optic sampling probe utilizes an electro-optic probe that makes use of this principle.
The electro-optic sampling oscilloscopes (hereinafter shortened to EOS oscilloscopes), have the following remarkable features compared with conventional sampling oscilloscopes using electric probes.
(1) The signal is easily measured since a ground wire becomes unnecessary when the measurement is performed.
(2) A high input impedance can be obtained since the metal pin on the tip of the electro-optic probe is insulated from the circuit system, and therefore, the point that is measured is not significantly disturbed.
(3) The measurement can be performed over a wide range of frequencies including the order of GHz since pulsed light is used (however, continuous light can also be used).
The structure of a conventional electro-optic probe which is used for signal measurement by an EOS oscilloscope will be explained with reference to FIG. 2. In FIG. 2, reference numeral 1 denotes a probe-head made of an insulator, and a metal pin 1a is set in the center thereof. Reference numeral 2 denotes an electro-optic element, and a reflection film 2a is provided on the end surface of the electro-optic element 2 so as to face and contact with the metal pin 1a. Reference numerals 3 and 8 denote collimator lenses, reference numeral 4 denotes a xc2xc wavelength plate, and reference numerals 5 and 7 denote polarizing beam splitters. Reference numeral 6 denotes a Faraday element for rotating a plane of polarization of an incident light by an angle of 45 degrees. Reference numeral 9 denotes a laser diode for emitting a laser beam in accordance with a control signal which is output by a pulse generating circuit (not shown) of an EOS oscilloscope main body 19. Reference numerals 10 and 11 denote collimator lenses, and reference numerals 12 and 13 denote photodiodes for outputting an electric signal corresponding to the input laser beam to the EOS oscilloscope main body 19. Furthermore, reference numeral 14 denotes a separator which is composed of the xc2xc wavelength plate 4, polarizing beam splitters 5, 7, and Faraday element 6; and reference numeral 15 denotes the main body of the probe, made of an insulator.
Next, the light pathway of the laser beam which is emitted by the laser diode 9 will be explained with reference to FIG. 2. In FIG. 2, reference number A denotes the light path of the laser beam.
The laser beam emitted by the laser diode 9 is converted to a parallel light beam by the collimator lens 8 and goes straight through the polarizing beam splitter 7, Faraday element 6, and polarizing beam splitters 5. The laser beam is further passed through the xc2xc wavelength plate 4 and collected by the collimator lens 3, and enters into the electro-optic element 2. This laser beam is reflected by the reflection film 2a which is provided on the end surface of the electro-optic element 2 which faces the metal pin 1a. 
The reflected laser beam is converted to a parallel light beam again by the collimator lens 3 and passes through the xc2xc wavelength plate 4. A part of this laser beam is reflected by the polarizing beam splitter 5 and enters the photodiode 12, and the laser beam which passes through the polarizing beam splitter 5 is reflected by the polarizing beam splitter 7 and entered into the photodiode 13. Here, the intensities of the laser beams which enter the photodiodes 12, 13 are adjusted by the xc2xc wavelength plate 4 so as to the same level.
Next, the operation for measuring the measured signal using the electro-optic probe shown in FIG. 2 will be explained.
When the metal pin 1a contacts the measured point, change in the electric field around the metal pin 1a caused by the voltage which is applied to the metal pin 1a is transmitted to the electro-optic element 2, and the double refractive index of the electro-optic element 2 is varied by the Pockels effect. As a result, the polarization of the laser beam changes when the laser beam enters and is transmitted through the electro-optic element 2. The laser beam, with a changed polarization, is reflected by the reflection film 2a and enters the photodiodes 12, 13, and converted to an electric signal.
Namely, the change in polarization of the laser beam, according to the change in voltage at the measured point, is converted to a difference between the output signals of the photodiodes 12, 13 by means of the electro-optic element 2, and the electric signal which is applied to the metal pin 1a can be measured by detecting this difference.
Furthermore, in the electro-optic probe as described above, the electric signals from the photodiodes 12, 13 are input and processed in the EOS oscilloscope. However, the measured signal can be also observed by connecting a conventional measuring instrument, such as a real-time oscilloscope, to the photodiodes 12, 13 via an exclusive controller. As described above, the measurement of electric signals using the electro-optic probe can be easily performed over a wide range of frequencies.
However, in a conventional electro-optic probe, since the metal pin 1a contacts the measured point as described above, electric field cannot be measured without disturbing the electric field. Thus, it is possible to improve on conventional electro-optic probes in this point.
The present invention is provided in consideration of the above circumstances, and an object of the present invention is to provide an electro-optic probe which can measure the electric field without disturbing the electric field, and a magneto-optic probe which is provided by partly changing the electro-optic probe and can measure the magnetic field without disturbing the magnetic field.
In order to achieve these objects, the first aspect of the present invention is an electro-optic probe comprising: a laser diode for emitting a laser beam in accordance with a control signal from a measuring instrument main body, an electro-optic element, provided with a reflection film on an end surface thereof, a separator provided between the laser diode and electro-optic element, and which is pervious to the laser beam emitted by the laser diode and separates a beam reflected from the reflection film, two photodiodes which transform the beam reflected by the separator into an electric signal, and a weak dielectric substance used for protecting the electro-optic element.
In this electro-optic probe, the weak dielectric substance can be made of glass, for example.
The second aspect of the present invention is an electro-optic probe comprising:, a laser diode for emitting a laser beam in accordance with a control signal from a measuring instrument main body, an electro-optic element, provided with a reflection film on an end surface thereof, a separator provided between the laser diode and electro-optic element, and which is pervious to the laser beam emitted by the laser diode and separates a beam reflected from the reflection film, and two photodiodes which transform the beam reflected by the separator into an electric signal, wherein the electro-optic element is exposed to the outside of the probe.
Furthermore, the first aspect of the present invention is a magneto-optic probe comprising: a laser diode for emitting a laser beam in accordance with a control signal from a measuring instrument main body, a magneto-optic element, provided with a reflection film on an end surface thereof, a separator provided between the laser diode and magneto-optic element, and which is pervious to the laser beam emitted by the laser diode and separates a beam reflected from the reflection film, two photodiodes which transform the beam reflected by the separator into an electric signal, and a weak dielectric substance used for protecting the magneto-optic element.
In this magneto-optic probe, the weak dielectric substance can be made of a glass, for example.
The second aspect of the present invention is a electro-optic probe comprising:, a laser diode for emitting a laser beam in accordance with a control signal from a measuring instrument main body, a magneto-optic element, provided with a reflection film on an end surface thereof, a separator provided between the laser diode and magneto-optic element, and which is pervious to the laser beam emitted by the laser diode and separates a beam reflected from the reflection film, and two photodiodes which transform the beam reflected by the separator into an electric signal, wherein the magneto-optic element is exposed to the outside of the probe.